Clément Foucault
83ac8628c4
This modifies the principled BSDF and the Glass BSDF which now have better fit to multiscatter GGX. Code to generate the LUT have been updated and can run at runtime. The refraction LUT has been changed to have the critical angle always centered around one pixel so that interpolation can be mitigated. Offline LUT data will be updated in another commit This simplify the BTDF retreival removing the manual clean cut at low roughness. This maximize the precision of the LUT by scalling the sides by the critical angle. I also touched the ior > 1.0 approximation to be smoother. Also incluse some cleanup of bsdf_sampling.glsl
109 lines
3.3 KiB
GLSL
109 lines
3.3 KiB
GLSL
|
|
#pragma BLENDER_REQUIRE(bsdf_common_lib.glsl)
|
|
|
|
/* ---------------------------------------------------------------------- */
|
|
/** \name Utiltex
|
|
*
|
|
* Utiltex is a sampler2DArray that stores a number of useful small utilitary textures and lookup
|
|
* tables.
|
|
* \{ */
|
|
|
|
uniform sampler2DArray utilTex;
|
|
|
|
#define LUT_SIZE 64
|
|
|
|
#define LTC_MAT_LAYER 0
|
|
#define LTC_BRDF_LAYER 1
|
|
#define BRDF_LUT_LAYER 1
|
|
#define NOISE_LAYER 2
|
|
#define LTC_DISK_LAYER 3 /* UNUSED */
|
|
|
|
/* Layers 4 to 20 are for BTDF Lut. */
|
|
const float lut_btdf_layer_first = 4.0;
|
|
const float lut_btdf_layer_count = 16.0;
|
|
|
|
/**
|
|
* Reminder: The 4 noise values are based of 3 uncorrelated blue noises:
|
|
* x : Uniformly distributed value [0..1] (noise 1).
|
|
* y : Uniformly distributed value [0..1] (noise 2).
|
|
* z,w : Uniformly distributed point on the unit circle [-1..1] (noise 3).
|
|
**/
|
|
#define texelfetch_noise_tex(coord) texelFetch(utilTex, ivec3(ivec2(coord) % LUT_SIZE, 2.0), 0)
|
|
|
|
/* Return texture coordinates to sample Surface LUT. */
|
|
vec2 lut_coords(float cos_theta, float roughness)
|
|
{
|
|
vec2 coords = vec2(roughness, sqrt(1.0 - cos_theta));
|
|
/* scale and bias coordinates, for correct filtered lookup */
|
|
return coords * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
|
|
}
|
|
|
|
/* Returns the GGX split-sum precomputed in LUT. */
|
|
vec2 brdf_lut(float cos_theta, float roughness)
|
|
{
|
|
return textureLod(utilTex, vec3(lut_coords(cos_theta, roughness), BRDF_LUT_LAYER), 0.0).rg;
|
|
}
|
|
|
|
/* Return texture coordinates to sample Surface LUT. */
|
|
vec3 lut_coords_btdf(float cos_theta, float roughness, float ior)
|
|
{
|
|
/* ior is sin of critical angle. */
|
|
float critical_cos = sqrt(1.0 - ior * ior);
|
|
|
|
vec3 coords;
|
|
coords.x = sqr(ior);
|
|
coords.y = cos_theta;
|
|
coords.y -= critical_cos;
|
|
coords.y /= (coords.y > 0.0) ? (1.0 - critical_cos) : critical_cos;
|
|
coords.y = coords.y * 0.5 + 0.5;
|
|
coords.z = roughness;
|
|
|
|
coords = saturate(coords);
|
|
|
|
/* scale and bias coordinates, for correct filtered lookup */
|
|
coords.xy = coords.xy * (LUT_SIZE - 1.0) / LUT_SIZE + 0.5 / LUT_SIZE;
|
|
|
|
return coords;
|
|
}
|
|
|
|
/* Returns GGX BTDF in first component and fresnel in second. */
|
|
vec2 btdf_lut(float cos_theta, float roughness, float ior)
|
|
{
|
|
if (ior <= 1e-5) {
|
|
return vec2(0.0);
|
|
}
|
|
|
|
if (ior >= 1.0) {
|
|
vec2 split_sum = brdf_lut(cos_theta, roughness);
|
|
float f0 = f0_from_ior(ior);
|
|
/* Baked IOR for GGX BRDF. */
|
|
const float specular = 1.0;
|
|
const float eta_brdf = (2.0 / (1.0 - sqrt(0.08 * specular))) - 1.0;
|
|
/* Avoid harsh transition comming from ior == 1. */
|
|
float f90 = fast_sqrt(saturate(f0 / (f0_from_ior(eta_brdf) * 0.25)));
|
|
float fresnel = F_brdf_single_scatter(vec3(f0), vec3(f90), split_sum).r;
|
|
/* Setting the BTDF to one is not really important since it is only used for multiscatter
|
|
* and it's already quite close to ground truth. */
|
|
float btdf = 1.0;
|
|
return vec2(btdf, fresnel);
|
|
}
|
|
|
|
vec3 coords = lut_coords_btdf(cos_theta, roughness, ior);
|
|
|
|
float layer = coords.z * lut_btdf_layer_count;
|
|
float layer_floored = floor(layer);
|
|
|
|
coords.z = lut_btdf_layer_first + layer_floored;
|
|
vec2 btdf_low = textureLod(utilTex, coords, 0.0).rg;
|
|
|
|
coords.z += 1.0;
|
|
vec2 btdf_high = textureLod(utilTex, coords, 0.0).rg;
|
|
|
|
/* Manual trilinear interpolation. */
|
|
vec2 btdf = mix(btdf_low, btdf_high, layer - layer_floored);
|
|
|
|
return btdf;
|
|
}
|
|
|
|
/** \} */
|